Alpha-1 antitrypsin (AAT, α1-antitrypsin, or A1AT) deficiency is an inherited, autosomal codominant genetic disorder that causes misfolding of the AAT protein and poor secretion of the misfolded protein leading to lung and liver diseases. AAT deficiency (AATD) occurs with a frequency of about 1 in every 1,500 to 3,500 individuals and most often affects persons with European ancestry.
Alpha-1 Antitrypsin is a protease inhibitor belonging to the serpin superfamily. Normal AAT protein is a circulating glycoprotein protease inhibitor primarily synthesized in the liver by hepatocytes and secreted into the blood. The known physiologic function of AAT is to inhibit neutrophil proteases, which serves to protect host tissues from non-specific injury during periods of inflammation.
The most clinically significant form of AATD, a genetic disorder associated with liver disease in children and adults, and pulmonary disease in adults, is caused by the Z mutation. The Z mutant allele (PiZ), through a single point mutation, renders the mutant Z form AAT protein (the “Z-AAT protein”) prone to abnormal folding causing intracellular retention. The mutant Z-AAT protein monomers are able to form chains of polymers that amass into aggregates, which are sometimes referred to as “globules.” The misfolded Z-AAT protein is ineffective in traversing the secretory pathway, and instead polymerizes and accumulates in the endoplasmic reticulum (ER) of hepatocytes. The polymeric globule masses stress the ER and trigger continuous hepatocyte injury, leading to fibrosis, cirrhosis, and increased risk of hepatocellular carcinoma. Further, the absence of circulating anti-protease activity leaves the lung vulnerable to injury by neutrophil elastase, resulting in the development of respiratory complications such as emphysema.
Individuals with the homozygous PiZZ genotype have severe deficiency of functional AAT, which leads to pulmonary disease. Weekly use of AAT augmentation therapy, using purified human AAT, results in near normal plasma levels of AAT in subjects with AATD, and helps prevent lung damage in affected individuals. However, while the administration of purified AAT can ameliorate or help prevent lung damage caused by the absence of endogenously secreted AAT, AATD patients remain vulnerable to endoplasmic reticulum liver storage disease caused by the deposition and accumulation of excessive abnormally folded AAT protein. Accumulated Z-AAT protein in the globule conformation in hepatocytes is a well-known characteristic of AATD liver disease and is believed to lead to proteotoxic effects that are responsible for inducing liver injury, including liver cell damage and death and chronic liver injury, in individuals with AATD. (see, e.g., D. Lindblad et al., Hepatology 2007, 46: 1228-1235). Patients with AATD often develop liver disease, which can be severe or fatal, even in infancy. Clinical presentations of injury in the liver include chronic hepatitis, cirrhosis, hepatocellular carcinoma, transaminitis, cholestasis, fibrosis, and even fulminant hepatic failure.
There is currently no clinically approved treatment to prevent the onset or slow the progression of liver disease due to AATD. Further, while U.S. Patent Application Publication No. 2015/0361427 discloses certain RNAi agents capable of inhibiting the expression of an AAT gene, there remains a need for novel and effective AAT RNAi agents having improved potency that can selectively, efficiently, and safely inhibit the expression of an AAT gene, thereby preventing and potentially reversing Z-AAT accumulation-related liver injury and fibrosis. Similarly, while U.S. Patent Application Publication No. 2015/0011607 to Brown et al. (“Brown '607”) discloses various sequences for inhibiting expression of an AAT gene, Brown teaches the use of longer double-stranded constructs (referred to in Brown as DsiRNAs), which according to Brown have been found to give “unexpected effective results in terms of potency and duration of action” as compared to 19-23mer siRNA agents. (See, e.g., Brown '607). Moreover, many of the sequences disclosed in Brown '607 are designed to be used in DsiRNA constructs that are designed to target different locations of an AAT mRNA as compared to the sequences disclosed in the present invention. Such differences lead to different binding affinity to the AAT mRNA and produces a different cleavage site, which can impact the inhibitory effect of the compound, while also potentially leading to additional off-target issues (see, e.g., Piotr J. Kamola et al., PLoS Comput Biol, 2015, 11(12):e1004656 at FIG. 1 (illustrating the mechanism of siRNA-Mediated Gene Silencing)). For example, nothing in Brown '607 teaches or suggests the design of an RNAi agent (of any length) wherein the 5′ terminal nucleobase or nucleotide of the antisense strand would be aligned with the position that is 19 nucleotides downstream (towards the 3′ end) from position 1000 on an AAT gene (SEQ ID NO: 1). Put different, and again solely as an example involving one such potential AAT RNAi agent sequence, nothing in Brown '607 teaches or suggests the design of an RNAi agent wherein the 5′ terminal nucleobase of the antisense strand of an RNAi agent corresponds to position 1018 on an AAT gene (SEQ ID NO: 1). Further, nothing in Brown '607 teaches or suggests the modified AAT RNAi agent constructs disclosed herein.